The conventional internal combustion engine has a high frictional, reciprocating piston due to the boundary lubrication. Our previous design in U.S. Pat. No. 5,437,220 inserts four sets of bearing grooves and recirculating ball bearings in the piston skirt to convert its sliding motion into the rotation of ball bearing and to reduce the frictional energy loss at the piston rings and skirt. However, the ball bearing piston is a modification from a conventional piston and is penalized for its obsolete piston skirt. It is hard to keep the weight light, and the assembly may create problem due to the difference in thermal expansion between the steel bearing groove and the aluminum piston skirt.
One natural way to solve these problems is to create a two piece piston with steel bearing grooves as the main piston skirt, and an original aluminum piston head. While the head retains part of the conventional skirt to hold on the piston pin, the new bearing groove structure rides on two steel rings over the piston pin independently. It provides the least weight and separates the steel bearing groove from the deleted aluminum piston skirt support.
Also, the previous design uses a compatible, hardened cylinder liner for the ball bearing to run. Although there are many balls to share the piston load, each ball has a small contact area which is just better than the point contact, and the contact stress will be high. A solution is to mill the cylinder liner to provide four lines of bearing track. These receded tracks have ball radius curvature and will enlarge the contact area against the ball bearing but minimize the extra blow-by.
1. Field of the Invention
This invention relates to the field of anti-friction piston and cylinder liner. The reduction of friction has achieved through a piston with rollers in the skirt, a two piece piston with cylindrical barrel rollers or a piston with recirculating ball bearings in our previous design.
2. Description of the Prior Art
Most of the prior patents utilized the rollers in the piston skirt or in the cylindrical barrel to withstand the piston thrust load under the peak firing pressure of the engine. Our previous patent uses numerous recirculating ball bearings. They all convert the sliding motion of a piston into the rotating motion.
U.S. Pat. No. 4,704,949, Piston. to John D. Foster in 1987 uses two sets of three roller bearings mounted on a light weight piston skirt. The load carrying capacity of three axles and rollers will limit the maximum allowable thrust load of the piston and the engine horsepower.
Our previous U.S. Pat. No. 5,437,220, Ball Bearing Piston in 1995 has the piston skirt milled to locate four sets of bearing grooves and recirculating ball bearings. The weight of piston will be increased and becomes a problem. The difference of thermal expansion of the aluminum piston skirt and steel bearing grooves creates concern or problem in the assembly. Also, the bearing groove serves perfectly as a ball bearing inner race. But the hardened cylinder liner has a mismatch curvature or nearly a point contact to the ball bearing. These concerns will limit the application.
In order to design a light weight ball bearing piston the bearing grooves become the main piston skirt structure. Two piece piston and modification on the cylinder liner are introduced to improve the ball bearing piston.